The genus Bdellovibrio represents a genetically diverse group of predatory bacteria which probably moderate the levels of bacteria in nature. The hunt down, attack, and kill other bacteria by penetrating their prey's outer membrane and peptidoglycan layer and by taking up residence in the periplasmic space. The prey cell becomes a modified growth chamber by providing shelter and all the required nutrition for the developmentally regulated growth phase of the predator. Intraperiplasmic bdellovibrios relocalize to their own outer membranes intact major outer membrane porin proteins purloined from their prey. The proposed research seeks the mechanisms employed by Bdellovibrio for this selective relocalization. Temporal and topological aspects of the relocalization process will be measured biochemically and by electron microscopy. A single mutation endows these highly adapted predators with the ability to grow axenically and express their own major outer membrane proteins. Thus, Bdellovibrio possess the genetic information for two modes of existence. The developmental biology of the bdellovibrois will be addressed by experiments which probe the relationship between the pillaged protein and the bdellovibrio-encoded outer membrane protein. The genetic organization of Bdellovibrio which permits the toggling between predatory and axenic modes will be accessed through studying the regulation of the bdellovibrio-encoded cell surface protein. The gene for the protein along with its regulatory sequences will be cloned. Sequence data will permit the construction of probes to locate the gene in strains which are normally shut off or leaky for protein expression. Sequencing regulatory regions and measuring mRNA levels from these genes will reveal mechanisms of developmental regulation employed by Bdellovibrio.